Fuel Pump Rewire for increased flow rates.
 

Not sure if this has been visited before but my Son recently brought it to my attention when we were discussing running a 200 shot of spray. He suggested that I use his nitrous test kit to ensure the fuel pressure remained constant when running a 200 fuel jet. So after a few minutes I soon found out that my 190 Walbro dropped to 30 psi, not good. He then mentioned that a lot pf VW and DSM guys rewired their fuel pump with a higher gauge wire to maintain a higher voltage. I measured the voltage at the pump with the engine running and found it to be just over 12v. I then ran a heavy gauge wire from the battery and conected it to the pump wire at the pump, the voltage went up to almost 14 and the fuel pressure went up by almost 10 psi.

So it was off to the store to buy some heavier wire. I decided on 10 gauge rather than something heavier because of the difficulty soldering heavier wire as well as routing. The stock wire at the pump is 14 gauge but if you strip the wire back a couple of feet you will find it increases to 12 gauge.

Thr easiest way is to run the heavier gauge wire directly from the battery with a fuse and use a relay to connect to the pump. Use the original pump supply wire to fire the relay and use the larger wire on the N.O contacts to run the pump.

Auto Performance has a couple of charts comparing 12v vs 13.8v and their corresponding flow rates and current draw.. Pretty impressive comparison. eg For my pump at 50 psi the flow rate increases from 36 to 46 gal/hr while the current draw remains the same.

I would suggest an adjustable FPR to compensate for the increased pressure.

A 255 pump was installed because even with the increased voltage the 190 pump would not handle a 200 shot. After installing the new pump my pressure increased to over 80 psi and took a lot of adjustment to bring it back into the 50 psi range.

Below are the two charts from their website.

http://jime.f-sw.com/Race2008/12.jpg
http://jime.f-sw.com/Race2008/13.5.jpg

Hey, this is good information. Mardi knew this - I sent him the heavy-wire pigtail from my Walbro 255lph pump so he could boost the voltage to his pump. I think it worked for him. Darn, now I wish I had kept it.

But I need to do this anyway, so Jim, your timing is good - for me. :) The relay mod will be easy - and add some serious safety to spraying...

Are you getting ready to make nitrous history with a 200-shot?

wow...great info...oman i was in ontario last month....couldnt access the internet with my phone......grrrr...could of met up with a few org members!

I remember having this problem so I bought a incabin fuel psi gauge to verify that my stock pump was not able to maintain psi while on nitrous and installed a 255 and havn't had a problem since

but then again I am only spraying a 100shot :(

Jime I do not know where your battery is located but if it's in the trunk run it from there the short wire will help due to lower resistance and try to use wire with a higher strain count but I am pretty sure you already know about the whole X number of feet = X amount of resistance and the effects of different strain counts have on current and voltage drop